Geographic theory in whale beaching
Researchers from the University of WA believe cyclone Marcus and Hamelin Bay’s gently sloping coastline caused the mass stranding of short-finned pilot whales last Friday.
More than 150 whales were stranded last Thursday night, and authorities were notified by a commercial fisherman at 6am on Friday.
UWA physics research associate Shane Chambers said Hamelin Bay’s topography and cyclone Marcus affecting the Leeuwin Current contributed to the mass stranding.
“This is a very unfortunate confluence of events where first you get a shallow sloping bay disrupting the bio-sonar they use for navigation, making the beach appear as a ‘deaf spot’,” he said.
“Hamelin Bay has a slope of about three degrees, compared to places like Scarborough Beach that have a slope of 20-30 degrees, so the low angle absorbs the whale’s ‘clicks’ and they don’t get an echo back.”
Mr Chambers said strandings generally occurred in April and May, but it was a coincidence Friday’s event was the exact same day as the 2009 beaching in which 76 out of 80 whales died.
“We had three cyclone systems over the north of Australia last week, which plays a role in the Leeuwin Current,” he said.
“The conditions would have likely created a very dense population of microbubbles in the water which further extinguishes the whale bio-sonar.”
Department of Biodiversity, Conservation and Attractions Blackwood district officer Ben Tannock said there was no confirmed reason why whales beached.
“Short and long-finned pilot whales are notorious for beaching,” he said.
“It’s always a baffling mystery of nature and we wonder why seemingly healthy animals beach themselves.”
On Friday evening, wildlife officers, with the help of volunteers and local contractors, removed the carcasses from the beach, and released seven whales further out to sea.
Mr Tannock said four of the seven did not seem to beach again, but five more carcasses washed ashore at the weekend, and were removed from areas north of Hamelin Bay, along the Boranup Beach stretch.
“Testing confirms the species, and adds to a DNA database of the short-finned pilot whales to better understand the species,” he said.
DBCA said it had “no plans”, such as beach netting, to avoid future strandings.
“That certainly hasn’t been discussed,” he said.
Mr Chambers said his research team had made equipment years ago that would be deployed into bays and send “alarm bells” to pods of whales that were approaching the shore.
“The problem is, the technology has been morphed into shark detection systems and was sold commercially,” he said.
He said the cost for producing and deploying the equipment for whales was too expensive, and because beachings happened infrequently, it would take more than two decades to collect data to confirm it worked.
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